1. Field of the Invention
The present invention relates to a color camera of a surface-sequence system to perform color separation by the use of a rotational filter.
2. Related Background Art
Traditionally, a color camera of a surface-sequence system uses a rotational filter to separate the incident light from an object into the light compositions of three primary colors, red, green, and blue.
The rotational filter comprises three filtering parts (hereinafter referred to as R, G, and B respectively) formed by dividing the circular filter into three regions each with a 1/3 circle to transmit red light, green light, and blue light respectively while shielding any other light.
Then, by transmitting an object image converged by an optical lens through the rotational filter to form its image on the image pick up plane of an image pick up element, image signals are obtained. With the rotation of the rotational filter, the object image is allowed to pass sequentially through each of R, G, and B parts of the filter. Accordingly, the image having each of the light compositions, red, green, and blue, of the object image can sequentially be formed on the image pick up element.
The image pick up element converts the image thus formed with each of the light compositions, red (R), green (G), and blue (B) into the respective electrical color signal (R signal, G signal, and B signal) and outputs each of them sequentially. Each color signal is amplified by an amplifier. The amplifier employed is capable of varying its amplification factor.
Then, in order to correct the particular characteristics of the image pick up element against each of the color signals, shading correction signals are generated by a correcting signal generating CKT, thereby varying the amplification factors to correct the image signals.
In the conventional technique set forth above, the image pick up is performed by one image pick up element, and particular shading corrections required for the image pick up optical system and image pick up element are performed for each of the R, G, and B color signals in the same fashion.
There is a problem encountered, however, that the correction cannot be made accurately when the same shading correction is applied to each of the R, G, and B color signals because the light transmission factors of the material of the rotational filter 1 are not even, and at different positions on the rotational filter 1 the transmission factors vary.